1. Field of the Invention
The present invention relates to a screw compressor and, more particularly, to a screw compressor used for a refrigeration cycle, which is well suited for decreasing the oil outflow amount (the amount of oil flowing out of the compressor).
2. Description of the Prior Art
There has been known an oil separator in which oil contained in gas discharged from a compressing mechanism section is separated and recovered by the centrifuging.operation, as is disclosed in JP-A-7-243391, for example. This type of oil separator is called as a cyclone type oil separator. The cyclone type oil separator is configured so as to introduce gas discharged from a compressor into a cyclone type of oil separating space section provided above an oil reservoir, where the oil is separated firstly by using the centrifugal force, and thereafter fine oil mist is separated secondarily in an oil collection chamber.
In the centrifugal separation type oil separator, the oil separating space section and the oil reservoir are generally constructed integrally. The oil is put on a wall surface by the centrifugal force induced by a whirling flow in the oil separating space section, drops along the inside wall while whirling, and is accumulated in the oil reservoir provided below the oil separating space section. The gas is discharged to the outside through a discharge pipe communicated with the oil separating space section.
In the above centrifugal separation type of oil separator, since the oil separating space section and the oil reservoir are constructed integrally, it is necessary to increase the distance between an oil surface in the oil reservoir and an inlet of the discharge pipe (hereinafter referred to as a space distance above the oil surface) in order to for ensure the high separation efficiency, and thus, it has been difficult to decrease the size of the oil separator. On the contrary, in the case of decreasing the size of the oil separator, it is necessary to decrease the space distance above the oil surface for securing a necessary amount of oil to be retained. As a result, there has been a drawback that the oil outflow amount increases remarkably by a whirling flow produced by the suction of the gas into the discharge pipe.
Further, in the above conventional oil separator, since the whirling flow in the oil separating space section causes the remarkable fluctuation of the oil level, there has been a problem that it is difficult to control the quantity of the residual oil in the compressor by using an oil level visual observation means such as a sight glass.
It is an object of the present invention to provide a screw compressor capable of decreasing the oil outflow amount (the amount of oil flowing out of the compressor) by adopting a small and simple construction.
It is a further object of the present invention to provide a screw compressor provided with an oil separator well suited for visually observing the oil level of the residual oil in the compressor.
In order to achieve the above objects, according to one aspect of the present invention, there is provided a screw including: a pair of male and female screw rotors which mesh with each other; a bearing for supporting the rotors; a motor for driving the rotors; a casing for housing the rotors, the bearing and the motor; a discharge passage through which refrigerant gas compressed by the screw rotors is discharged; an oil separating space section communicated with the discharge passage; an oil reservoir for accumulating oil separated in the oil separating space section; and a discharge port provided so as to communicate with the oil separating space section for discharging the gas from which the oil is separated in the oil separating space section, wherein the oil separating space section is of a cylindrical shape; the discharge passage is connected to the cylindrical oil separating space section substantially in the tangential direction; and the lower part of the oil separating space section is connected to the oil reservoir through a communication passage having a passage area smaller than the cross-sectional area of the oil separating space section.
Preferably, a cylindrical member concentric with the oil separating space section may be provided so that the discharge port is communicated with the inside space of the.cylindrical member, and the discharge passage may be communicated with a space between the inside wall of the cylindrical oil separating space section and the cylindrical member.
According to further aspect of the present invention, there is also provided a screw compressor including: a male rotor and a female rotor which mesh with each other; a discharge passage for compressed gas to be discharged from the male and female rotors; an oil separating space section for separating oil from the compressed gas discharged from the discharge passage; an oil reservoir for accumulating the separated oil; and a casing for housing the male and female rotors, the discharge passage, the oil separating space section, and the oil reservoir, wherein the oil separating space section is of a cylindrical shape; a discharge port is provided at the upper part of the oil separating space section for introducing the gas to the outside thereof; the oil separating space section is provided with a cylindrical member concentric therewith so that the discharge port communicates with the inside space of the cylindrical member; the discharge passage is connected to the cylindrical oil separating space section in the tangential direction; and the oil separating space section and the oil reservoir are connected to each other through a communication passage having a cross-sectional area smaller than that of the cylindrical portion of the oil separating space section.
According to another aspect of the present invention, there is further provided a screw compressor including: a main casing for housing a male rotor and a female rotor which mesh with each other, a bearing, and a motor; a discharge casing having a discharge passage through which refrigerant gas compressed by the male and female rotors is discharged, an oil separating space section communicated with the discharge passage, and a discharge port; and an oil reservoir provided at the lower part of the oil separating space section, wherein the oil separating space section provided in the discharge casing is of a cylindrical shape; the cylindrical oil separating space section is provided with a cylindrical member concentric therewith so that the discharge port communicates with the inside space of the cylindrical member; the discharge passage has an opening configured so that the refrigerant gas flows along the inside wall surface of the cylindrical oil separating space section; and the screw compressor further comprises a communication passage through which the lower part of the oil separating space section and the oil reservoir are connected to each other, the communication passage being configured so as to have a passage area smaller than the cross-sectional area of the cylindrical portion of the oil separating space section.
Preferably, the oil reservoir may be formed integrally with the main casing in the lower part of the main casing. Also, the communication passage for communicating the oil separating space section with the oil reservoir may be provided at the lower end of the oil separating space section. Further, the bottom part of the oil separating space section may be formed into a substantially conical shape or configured to have a substantially spherical curve. In the case that the bottom part of the oil separating space section is formed into a conical shape, a spiral groove may be provided on the inside wall of the conical oil separating space section. Furthermore, the oil reservoir may be provided with a device for visually observing or detecting the oil level in the oil reservoir, such as a sight glass.
In order to miniaturize the compressor and achieve the sufficient oil separation effect, the volume of the oil separating space section may be 0.015 to 0.020% of the compressor discharge quantity per hour.
An embodiment of the present invention will now be described with reference to the accompanying drawings.